Motor and disk drive apparatus

ABSTRACT

A rotary unit of a motor includes a tubular hub portion. A bearing mechanism of the motor includes a bearing portion positioned radially inward of the hub portion. A stationary unit of the motor includes a stator fixing portion positioned inward of the hub portion and higher than a lower end of the hub portion. A cylinder gap is defined between the hub portion and an upper section of the bearing portion. A first communication gap is defined between a lower section of the hub portion and an upper section of the stator fixing portion. A second communication gap is defined between the lower end of the hub portion and a radial inner section of the stator core.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric motor and more specificallyto a disk drive apparatus provided with the motor.

2. Description of the Related Art

Conventionally, a spindle motor is mounted to a disk drive apparatussuch as a hard disk drive. A conventional brushless motor disclosed inJapanese Patent Application Publication No. 2007-295666 includes anattachment plate, a substantially cylindrical bushing, a thrust plate, asleeve, and a shaft. The bushing is fitted to a fixing hole of theattachment plate. The thrust plate is fixed to the lower portion of thebushing. The sleeve is made of an oil-impregnated sintered material andis press-fitted to the inner circumferential surface of the bushing. Theshaft is inserted into the sleeve. The shaft is supported in the radialdirection by the sleeve and is supported in the thrust direction by athrust washer arranged on the upper surface of the thrust plate.

A conventional motor for disk devices disclosed in Japanese PatentApplication Publication No. 2003-153481 includes a bracket, a bearing asa ball bearing, a rotor, and a stator. The bracket is fixed to a chassisof a disk device. The bracket includes an inner cylinder portionextending in the axial direction. The bearing is fixed to the inside ofthe inner cylinder portion. A shaft portion of a rotor is rotatablysupported by the bearing. A stator core of a stator is fixed to theouter circumferential surface of the inner cylinder portion. The innercircumferential portion of the stator core contacts the bottom surfaceportion of the bracket. Coils are formed in the outer circumferentialportion of the stator core. The outer circumferential portion of thestator core is positioned axially above the inner circumferentialportion thereof. Since the outer circumferential portion of the statorcore is separated from the bottom surface portion, it is possible toprevent the coils and the bottom surface portion from interfering witheach other.

However, in a motor in which a rotary unit is rotatably supported by alubricant, it is necessary to suppress vaporization of a lubricant heldwithin a bearing mechanism.

SUMMARY OF THE INVENTION

A motor in accordance with a preferred embodiment of the presentinvention includes a stationary unit, a rotary unit, and a bearingmechanism. The bearing mechanism is arranged to support the rotary unitso as to rotate with respect to the stationary unit about a center axisextending in an up-down direction. The rotary unit includes a coverportion extending around the center axis, a sidewall portion, a hubportion, and a rotor magnet. The sidewall portion extends downward froman outer edge of the cover portion. The hub portion protrudes downwardfrom the cover portion at a radial inner side of the sidewall portion.The rotor magnet is fixed to an inner circumferential surface of thesidewall portion.

The bearing mechanism includes a shaft portion and a bearing portion.The shaft portion extends downward from the cover portion along thecenter axis. The bearing portion to which the shaft portion is insertedis arranged to support the shaft portion through a lubricant. Thebearing portion includes an upper section positioned radially inward ofthe hub portion.

The stationary unit includes a stator, a base portion, and a statorfixing portion. The stator is positioned radially inward of the rotormagnet. The base portion is positioned below the stator. The statorfixing portion extends upward from a central portion of the baseportion. The stator fixing portion includes an upper end positionedradially inward of the hub portion and axially higher than a lower endof the hub portion.

The stator includes a stator core and a plurality of coils. The statorcore includes an annular core-back and a plurality of teeth portions.The core-back is arranged below the hub portion. The teeth portionsextend radially outward from the core-back. The coils are arrangedaround the teeth.

Each of the teeth portions includes a coil winding portion wound witheach of the coils and a slanted portion extending radially outward andupward.

A seal region in which a boundary surface of the lubricant is providedis defined between the upper section of the bearing portion and therotary unit. A substantially cylindrical cylinder gap is defined betweenan inner circumferential surface of the hub portion and an outercircumferential surface of the upper section of the bearing portion.

A first communication gap is defined between a lower section of the hubportion and an upper section of the stator fixing portion. The firstcommunication gap includes a section extending in an axial direction orinclined radially outward and downward. Further, a second communicationgap is defined between the lower end of the hub portion and a radialinner section of the stator core. The second communication gap extendsradially outward from the first communication gap.

With the motor in accordance with preferred embodiments of the presentinvention, it is possible to significantly reduce and preventvaporization of a lubricant held within a bearing mechanism of themotor.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a disk drive apparatus according to arelated preferred embodiment of the present invention.

FIG. 2 is a sectional view showing a motor in accordance with apreferred embodiment of the present invention.

FIG. 3 is a bottom view showing a base portion and a substrate inaccordance with a preferred embodiment of the present invention.

FIG. 4 is a sectional view of the motor in accordance with a preferredembodiment of the present invention.

FIG. 5 is a sectional view showing a substrate insertion hole inaccordance with a preferred embodiment of the present invention on anenlarged scale.

FIG. 6 is a sectional view showing a motor according to one modifiedexample of a preferred embodiment of the present invention.

FIG. 7 is a bottom view showing a base plate and a substrate inaccordance with a preferred embodiment of the present invention.

FIG. 8 is a sectional view showing a motor according to another modifiedexample of a preferred embodiment of the present invention.

FIG. 9 is a plan view showing a stator core of a motor according toanother preferred embodiment of the present invention.

FIG. 10 is a sectional view of the stator core in accordance with apreferred embodiment of the present invention.

FIG. 11 is a plan view of the stator core in accordance with a preferredembodiment of the present invention.

FIG. 12 is a plan view of a stator core of a motor according to afurther related preferred embodiment of the present invention.

FIG. 13 is a plan view of a base plate in accordance with a preferredembodiment of the present invention.

FIG. 14 is a plan view of the base plate and the stator core inaccordance with a preferred embodiment of the present invention.

FIG. 15 is a plan view showing another example of the stator core inaccordance with a preferred embodiment of the present invention.

FIG. 16 is a sectional view showing a motor according to a firstpreferred embodiment of the present invention.

FIG. 17 is a sectional view showing a motor according to one modifiedexample of the first preferred embodiment of the present invention.

FIG. 18 is a sectional view showing a motor according to a secondpreferred embodiment.

FIG. 19 is a plan view showing another example of the stator core inaccordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, the upper side in FIG. 1 along the centeraxis direction of a motor will be just referred to as “upper” and thelower side as “lower”. The up-down direction is not intended to indicatethe positional relationship and orientation of the motor installed in anactual device. The direction parallel to or substantially parallel tothe center axis will be referred to as “axial”. The radial directionabout the center axis will be just referred to as “radial”. Thecircumferential direction about the center axis will be just referred toas “circumferential”.

FIG. 1 is a vertical sectional view of a disk drive apparatus 1including a spindle motor 12 according to a related preferred embodimentof the present invention of the present invention. In the followingdescription, the spindle motor 12 will be just referred to as “motor12”. The disk drive apparatus 1 is, e.g., a hard disk drive. The diskdrive apparatus 1 can be mounted to a so-called tablet personalcomputer, for example. The disk drive apparatus 1 preferably includes adisk 11, a motor 12, an access unit 13, a housing 14, and a clamper 151.The motor 12 rotates the disk 11 which is arranged to recordinformation. The access unit 13 performs at least one of an informationreading task and an information recording task with respect to the disk11.

The housing 14 preferably includes a cup-shaped first housing member 141and a plate-shaped second housing member 142. The disk 11, the motor 12,the access unit 13, and the clamper 151 are accommodated within thefirst housing member 141. The second housing member 142 is fitted to thefirst housing member 141, thereby defining the housing 14. Preferably,the internal space of the disk drive apparatus 1 is a clean space inwhich dust or dirt is either not present or is extremely rare. Air ispreferably filled in the internal space of the disk drive apparatus 1.Alternatively, a helium gas, a hydrogen gas or a mixture of the heliumgas and/or the hydrogen gas with air, for example, may be filled in theinternal space of the disk drive apparatus 1. While not shown in FIG. 1,a flexible wiring substrate to be described later is preferably arrangedon the lower surface of the first housing member 141 in the disk driveapparatus 1.

The disk 11 is clamped to the motor 12 by the clamper 151. The accessunit 13 preferably includes a head 131, an arm 132 and a head movingmechanism 133. The head 131 is arranged adjacent to the disk 11 tomagnetically perform at least one of an information reading task and aninformation recording task. The arm 132 supports the head 131. The headmoving mechanism 133 moves the arm 132 so that the head 131 can be movedwith respect to the disk 11. With these configurations, the head 131gains access to a desired position on the rotating disk 11 in a statewhere the head 131 is kept in close proximity with the disk 11.

FIG. 2 is a vertical sectional view of the motor 12. The motor 12 ispreferably an outer-rotor-type three-phase motor. The motor 12preferably includes a stationary unit 2, a rotary unit 3, and a fluiddynamic pressure bearing mechanism 4. In the following description, thefluid dynamic pressure bearing mechanism 4 will be just referred to as“bearing mechanism 4”. The rotary unit 3 is supported by the bearingmechanism 4 so that the rotary unit 3 can rotate with respect to thestationary unit 2 about the center axis J1 extending in the up-downdirection of the motor 12.

The stationary unit 2 preferably includes a base plate 21 defining abase portion, a stator 22, and a flexible wiring substrate 23. In thefollowing description, the flexible wiring substrate 23 will be justreferred to as “substrate 23”. The base plate 21 is preferably a memberformed by pressing a metal plate member, however, any other type of baseplate could be used instead. The base plate 21 is preferably a portionof the first housing member 141 shown in FIG. 1. The base plate 21preferably includes a substrate insertion hole 51, a solder receptionhole and a stator fixing portion 211 a. The substrate insertion hole 51and the solder reception hole 52 are preferably through-holes extendingthrough the base plate 21 in the up-down direction. The substrate 23extends from the lower surface of the base plate 21 to the upper surfacethereof through the substrate insertion hole 51. The stator fixingportion 211 a preferably has a substantially cylindrical shape andextends upward from the central portion of the base plate 21. The baseplate 21 and the stator fixing portion 211 a are preferably formed by apress into a continuous monolithic member. Alternatively, the base plate21 may also be formed by casting.

The stator 22 is arranged above the base plate 21. The stator 22preferably includes a stator core 221 and a plurality of coils 222. Thestator core 221 is preferably provided by axially stacking a pluralityof electromagnetic steel plates 220, however, any other desirable typeof stator core could be used instead. The coils 222 are preferablyprovided by winding conductive wires on the stator core 221. The radialinner portion of the stator core 221 is fixed to the outercircumferential surface of the stator fixing portion 211a. Electricpower is supplied from an external power source to the stator 22 via thesubstrate 23.

The rotary unit 3 preferably includes a rotor hub 31 and a rotor magnet32. The rotor hub 31 preferably includes a cover portion 311, asubstantially cylindrical sidewall portion 312, and a disk mountingportion 313. The cover portion 311 is preferably defined by an annularshape about the center axis J1 and is positioned above the stator 22.The sidewall portion 312 extends downward from the outer edge of thecover portion 311. The disk mounting portion 313 extends radiallyoutward from the sidewall portion 312. The disk 11 shown in FIG. 1 ismounted on the disk mounting portion 313. The rotor magnet 32 is fixedto the inner circumferential surface of the sidewall portion 312 and ispositioned radially outward of the stator 22. As the electric power issupplied to the stator 22, torque is generated between the stator 22 andthe rotor magnet 32.

The bearing mechanism 4 preferably includes a shaft portion 41, a sleeve42, a sleeve housing 43, a thrust plate 44, a seal member 45, and alubricant 46. In the following description, the sleeve 42 and the sleevehousing 43 will be collectively referred to as “bearing unit 40”. Theshaft portion 41 extends downward from the radial inner section of thecover portion 311 in a coaxial or substantially coaxial relationshipwith the center axis J1. The shaft portion 41 and the rotor hub aredefined by a continuously-extending member. A female thread portion 411is provided on the inner surface of the shaft portion 41 over the wholelength of the shaft portion 41. At the center of the cover portion 311,a screw 152 shown in FIG. 1 is threadedly coupled to the female threadportion 411, whereby the clamper 151 is fixed to the motor 12.

The sleeve housing 43 is preferably a substantially cylindricalclosed-bottom member. The cylinder portion 431 of the sleeve housing 43is arranged inside the stator fixing portion 211 a. A tubular hubportion 314 protruding downward from the cover portion 311 is positionedat the radial inner side of the sidewall portion 312 and at the radialouter side of the stator fixing portion 211 a and the sleeve housing 43.A cylinder gap 474 having a substantially cylindrical shape is definedbetween the inner circumferential surface of the hub portion 314 and theupper section of the outer circumferential surface of the cylinderportion 431. The sleeve 42 is arranged on the inner circumferentialsurface of the sleeve housing 43. The shaft portion 41 is inserted intothe sleeve 42. The thrust plate 44 is preferably fixed to the shaftportion 41 by threadedly coupling a central thread portion thereof tothe lower extension of the female thread portion 411. The seal member 45is preferably adhesively bonded to the lower surface of the sleevehousing 43 and the lower surface 214 of the central portion 211 of thebase plate 21.

In the motor 12, the lubricant 46 is preferably continuously present inthe radial gap 471 between the inner circumferential surface of thesleeve 42 and the outer circumferential surface of the shaft portion 41,in the thrust gap 472 between the upper surface of the sleeve 42 and theupper surface of the sleeve housing 43 and the lower surface of thecover portion 311, in the gap 473 around the thrust plate 44 and in thecylinder gap 474. A seal region 474 a for holding the lubricant 46 isdefined in the cylinder gap 474.

Radial dynamic pressure groove arrays are preferably provided in theupper and lower sections of the inner circumferential surface of thesleeve 42. In the radial gap 471, a radial dynamic pressure bearingportion 481 is defined by the radial dynamic pressure groove arrays. Inthe thrust gap 472, a thrust dynamic pressure bearing portion 482 isdefined by a thrust dynamic pressure groove array. During the operationof the motor 12, the shaft portion 41 and the thrust plate 44 aresupported by the radial dynamic pressure bearing portion 481 and thethrust dynamic pressure bearing portion 482 without making contact withthe bearing unit 40. Thus, the rotary unit 3 is rotatably supported withrespect to the base plate 21 and the stator 22.

FIG. 3 is a bottom view illustrating only the base plate 21 and thesubstrate 23 of the motor 12. In FIG. 3, the substrate 23 is hatched byslanted parallel lines with a narrow gap. This also holds true in FIG.7. As shown in FIGS. 2 and 3, the lower surface of the base plate 21preferably includes a portion 213 inclined upward from the outer edge ofthe central portion 211 toward the radial outer side. In the followingdescription, the portion 213 will be referred to as “step portion 213”.The step portion 213 is preferably provided by a substantially annularshape about the center axis J1. A portion 212 existing radially outwardof the step portion 213 is positioned higher than the central portion211. In the following description, the portion 212 will be referred toas “peripheral portion 212”. In FIG. 3, the peripheral portion 212 ishatched by slanted parallel lines with a wide gap. The expression “stepportion” refers to a step-shaped portion including the periphery of theportion 213. For the sake of convenience in description, the portion 213will be called “step portion” herein. The portion arranged higher thanthe step portion 213 corresponds to the peripheral portion 212. Theportion arranged lower than the step portion 213 corresponds to thecentral portion 211.

The central portion 211 is preferably provided with a plurality ofsolder reception holes 52. The solder reception holes 52 are positionedradially inward of the substrate insertion hole 51. As shown in FIG. 3,the substrate insertion hole 51 axially overlaps with the step portion213. The lower opening of the substrate insertion hole 51 is included inthe step portion 213. FIG. 4 is a sectional view showing the substrate23 of the motor 12 and the surrounding structures on an enlarged scale.The substrate insertion hole 51 is preferably positioned radially inwardof the rotor magnet 32.

As shown in FIGS. 3 and 4, the substrate 23 preferably includes aconnection portion 231 and a lead portion 232. The connection portion231 preferably is substantially arc-shaped about the center axis J1. Theconnection portion 231 preferably includes a plurality of outlet holes231 b extending through the connection portion 231. The outlet holes 231b preferably axially overlap with the solder reception holes 52.

The lower surface of the connection portion 231 shown in FIG. 4 ispreferably bonded to the surrounding regions of the solder receptionholes 52 on the upper surface 215 of the central portion 211. All thesolder reception holes 52 preferably overlap with the connection portion231 in the up-down direction. The upper surface of the connectionportion 231 contacts the lower portions of the coils 222. An insulationfilm is preferably provided on the upper surface of the connectionportion 231, thereby providing insulation between the connection portion231 and the coils 222. Lead wires 223 led out from the coils 222 extendthrough the outlet holes 231 b and are soldered to the lower surface ofthe connection portion 231. The tip end portions of the lead wires 223are covered by solder portions 233, i.e., solder masses, which arearranged on the lower surface of the connection portion 231. The outletholes 231 b are preferably closed by the solder portions 233. All thesolder portions 233 are positioned within the solder reception holes 52.Preferably, an adhesive agent 24 exists in the entire regions of thesolder reception holes 52 and the substrate insertion hole 51. Thisprevents a gas from flowing into and out of the disk drive apparatusthrough the solder reception holes 52 and the substrate insertion hole51.

As shown in FIGS. 3 and 4, the upper surface of the lead portion 232 isarranged on the step portion 213 and the lower surface 216 of theperipheral portion 212. Preferably, the lead portion 232 is adhesivelybonded to the step portion 213 and the lower surface 216 of theperipheral portion 212 by a double-side tape or a sticky material, forexample. The axial distance between the lower surface 216 of theperipheral portion 212 and the lower surface 214 of the central portion211, i.e., the lowermost surface of the base plate 21, is preferablyequal to or larger than the axial thickness of the lead portion 232.This configuration helps prevent the lead portion 232 from protrudingdownward beyond the lowermost surface of the base plate 21.Alternatively, the upper surface of the lead portion 232 may be bondedto the step portion 213 and the lower surface 216 of the peripheralportion 212 by an adhesive agent, for example.

As stated above, the substrate insertion hole 51 shown in FIG. 4 ispreferably positioned radially inward of the rotor magnet 32. Thisprevents the substrate 23 from getting closer to the rotor magnet 32. Asa result, it is possible to prevent the rotor magnet 32 frommagnetically affecting the substrate 23. Since an annular plate 321 as amagnetic member is arranged on the lower surface of the rotor magnet 32,it is possible to prevent the magnetic flux from being leaked downwardfrom the rotor magnet 32. This configuration makes it possible tofurther prevent the rotor magnet 32 from magnetically affecting thesubstrate 23.

FIG. 5 is a view showing the substrate insertion hole 51 of the baseplate 21 on an enlarged scale. The adhesive agent is not shown in FIG.5. In the following description, the edge of the substrate insertionhole 51 near the upper surface 215 of the central portion 211, i.e., theedge of the substrate insertion hole 51 near the connection portion 231of the substrate 23, will be referred to as “upper edge 511”. The edgeof the substrate insertion hole 51 near the lower surface 216 of theperipheral portion 212, i.e., the edge of the substrate insertion hole51 near the lead portion 232 of the substrate 23, will be referred to as“lower edge 512”. The upper edge 511 preferably includes a slantedsurface 511 a connected to the upper surface 215 of the central portion211 and the inner circumferential surface 513 of the substrate insertionhole 51 parallel or substantially parallel to the center axis J1. Thelower edge 512 preferably includes a slanted surface 512 a connected tothe lower surface 216 of the peripheral portion 212 and the innercircumferential surface 513 of the substrate insertion hole 51.

When assembling the stationary unit 2, the lead portion 232 ispreferably inserted into the substrate insertion hole 51 from the upperside thereof. The connection portion 231 and the lead portion 232 aredisposed on the upper surface 215 of the central portion 211 and thelower surface 216 of the peripheral portion 212, respectively. Next, thestator core 221 shown in FIG. 4 is inserted into the stator fixingportion 211 a. The lead wires 223 of the coils 222 are inserted into theoutlet holes 231 b of the connection portion 231. The lead wires 223 aresoldered to the connection portion 231 within the solder reception holes52. The solder portions 233 close up the outlet holes 231 b. Theadhesive agent 24 is filled in the entire regions of the solderreception holes 52, thereby sealing the solder reception holes 52.Similarly, the substrate insertion hole 51 is sealed by the adhesiveagent 24. In the motor 12, the slanted surfaces 511 a and 512 a definedin the substrate insertion hole 51 make it possible to easily insert thelead portion 232 into the substrate insertion hole 51.

In the motor 12, the connection portion 231 of the substrate 23 isconnected to the stator 22 at the upper side of the lower surface 214 ofthe central portion 211 of the base plate 21. The solder portions 233defined in the connection portion 231 overlap with the solder receptionholes 52 in the up-down direction. Accordingly, even if the height ofthe motor 12 is reduced, the solder portions 233 are prevented fromprotruding downward from the base plate 21. The upper surface and thelower surface of the connection portion 231 are axially bonded to thecoils 222 and the base plate 21, respectively. This makes it possible toprevent the substrate 23 from moving in the up-down direction and to fixthe position of the substrate 23. Inasmuch as the substrate insertionhole 51 is positioned radially inward of the rotor magnet 32, the leadportion 232 is preferably prevented from getting closer to the rotormagnet 32. This makes it possible to prevent the rotor magnet 32 frommagnetically affecting the substrate 23.

Since the step portion 213 is formed into an annular shape by, forexample, a press work, the distance between the section of the uppersurface of the base plate 21 corresponding to the step portion 213 andthe rotor magnet 32 is preferably prevented from varying in thecircumferential direction. As a consequence, it is possible to prevent ageneration of a circumferential deviation in the magnetic attractionforce acting between the base plate 21 and the rotor magnet 32.

FIG. 6 is a sectional view showing a motor according to one modifiedexample of a preferred embodiment of the present invention. FIG. 7 is abottom view showing the base plate 21 and the substrate 23 of the motor12. A gap 9 is defined between the inner end of the connection portion231 of the substrate 23 and the radial inner edge of each of the solderreception holes 52.

When assembling the stationary unit 2, the upper surface of theconnection portion 231 shown in FIG. 6 is first adhesively bonded to thecoils 222. The lead wires 223 are soldered to the lower surface of theconnection portion 231. Next, the stator core 221 is preferably insertedinto the stator fixing portion 211 a. At this time, the lead portion 232is preferably inserted into the substrate insertion hole 51. The leadportion 232 is arranged on the lower surface 216 of the peripheralportion 212. Since the gaps 9 are defined between the inner end of theconnection portion 231 and the radial inner edges of the solderreception holes 52, the lead wires 223 are positioned within the solderreception holes 52 through the gaps 9. The solder portions 233 arepositioned within the solder reception holes 52. Preferably, an adhesiveagent 24 having an increased viscosity is filled in the solder receptionholes 52, thereby sealing the solder reception holes 52. Similarly, thesubstrate insertion hole 51 is sealed by the adhesive agent 24. In themotor 12 shown in FIG. 6, it is equally possible to reduce the height ofthe motor 12 by positioning the solder portions 233 within the solderreception holes 52. While the upper surface of the connection portion231 is preferably adhesively bonded to the coils 222, the presentinvention is not limited thereto. For example, the lower surface of theconnection portion 231 may be adhesively bonded to the upper surface 215of the central portion 211.

FIG. 8 is a sectional view showing a motor according to another modifiedexample of a preferred embodiment of the present invention. A singlelarge substrate insertion hole 53 is preferably defined in the baseplate 21. The connection portion 231 is preferably adhesively bonded tothe lower portions of the coils 222. The lead portion 232 is preferablyarranged below the base plate 21 through the substrate insertion hole53. The lead wires 223 led out from the coils 222 are soldered to thelower surface of the connection portion 231. All the solder portions 233are positioned within the substrate insertion hole 53. In the motor 12shown in FIG. 8, the substrate insertion hole 53 also serves as a solderreception hole.

In the motor 12 described above, the base plate 21 preferably has atleast one hole extending through the base plate in the up-downdirection. Accordingly, it is possible to guide the lead portion 232 tothe lower surface of the base plate while arranging the connectionportion 231 higher than the lower surface of the base plate 21. It isalso possible to have the solder portions 233 positioned within thehole. With this configuration, a reduction in the height of the motor 12is achieved. This holds true in all of the preferred embodiments to bedescribed later.

FIG. 9 is a plan view showing a stator core 221 a of a motor accordingto another related preferred embodiment of the present invention. Thestructures of the motor other than the stator core 221 a remain the sameas the structures of the motor 12 shown in FIG. 2. The stator core 221 apreferably includes an annular core-back 61 and a plurality of teethportions 62. In this regard, the core-back 61 refers to the annularportion of the stator core 221 a existing radially inward of the innerends of the gaps defined between the teeth portions 62. FIG. 10 is asectional view of the stator core 221 a taken along line A-A in FIG. 9.The right side in FIG. 10 corresponds to the radial outer side of thestator core 221 a. The stator core 221 a preferably includes a pluralityof electromagnetic steel plates 220 preferably formed by, for example, apress. In the following description, the electromagnetic steel plates220 will be called “core members 220”.

The core-back 61 shown in FIGS. 9 and 10 is preferably fixed by, forexample, an adhesive agent to the outer circumferential surface of thestator fixing portion 211 a shown in FIG. 2. The teeth portions 62extend radially outward from the core-back 61. Each of the teethportions 62 preferably includes a coil winding portion 621, a tip endportion 622, and an increased width portion 623. The coil windingportion 621 preferably is formed into a substantially straight shape toextend in the radial direction. A coil 222 indicated by a double-dotchain line in FIG. 10 is wound on the coil winding portion 621. The tipend portion 622 is preferably circumferentially widened from the radialouter end of the coil winding portion 621. The increased width portion623 is preferably arranged between the coil winding portion 621 and thecore-back 61 and provided as a single monolithic piece with the coilwinding portion 621 and the core-back 61. The tip end portion 622 andthe increased width portion 623 are preferably larger in circumferentialwidth than the coil winding portion 621.

The coil winding portion 621 preferably includes a caulking portion 621a arranged to fix a plurality of core members 220 together by caulking.The core-back 61 preferably includes a plurality of caulking portions611 and a cutout portion 612 shown in FIG. 9. The caulking portions 611are configured to fix the core members 220 together by caulking. Sincethe coil winding portion 621 and the core-back 61 of the stator core 221a are respectively provided with the caulking portion 621 a and thecaulking portions 611, the core members 220 are strongly fixed together.This helps prevent the core members 220 from being separated from oneanother in the teeth portions 62 and the core-back 61.

As shown in FIG. 9, the cutout portion 612 is preferably depressedradially outward from the inner circumferential surface of the core-back61. When the core members 220 are axially stacked one above another asshown in FIG. 10, the cutout portion 612 is used as a mark whichpositions the core members 220 in the circumferential direction. A slit625 extends radially between the increased width portions 623 adjoiningto each other. The slit 625 preferably radially overlaps with a slot gap626 defined between the tip end portions 622 adjoining to each other.The circumferential maximum width of the slit 625 is preferably smallerthan the width, i.e., the minimum width, of the slot gap 626.Alternatively, the maximum width of the slit 625 may be equal orapproximately equal to the width of the slot gap 626.

As shown in FIG. 10, the increased width portion 623 preferably includesa slanted portion 624 extending radially outward and upward from thecore-back 61. In the following description, the surface 624 a of theslanted portion 624 existing at the upper side in FIG. 10, i.e., thesurface whose normal line is inclined radially inward, namely leftwardin FIG. 10, and upward, will be referred to as “upper surface 624 a”.The slanted portion 624 is preferably formed by, for example, bendingthe stator core 221 a with a press. The thickness of the slanted portion624 in the direction perpendicular or substantially perpendicular to theupper surface 624 a of the slanted portion 624 is smaller than the axialthickness of the coil winding portion 621 and the core-back 61. Moreprecisely, the total thickness of the portions of the core members 220defining the slanted portions 624 is preferably smaller than the totalthickness of the portions of the core members 220 defining the coilwinding portions 621 and the core-backs 61. As a result, the thicknessof the slanted portion 624 that is actually used as a magnetic pathbecomes small.

FIG. 11 is an enlarged view showing the teeth portion positioned at theupper side in FIG. 9. The inner edge section 624 b of the slantedportion 624 is positioned radially outward of the inner edge section 623b of the increased width portion 623, i.e., radially outward of thesection existing between the inner ends of the two adjoining slits 625.In FIG. 11, the inner edge section 623 b of the increased width portion623 is indicated by a broken line. The outer edge section 624 c of theslanted portion 624 and the outer edge section 623 c of the increasedwidth portion 623 are preferably arc-shaped about the center axis J1.The circumferential width of the tip end portion 622 is a slantedportion larger than the circumferential maximum width of the increasedwidth portion 623. When seen in a plan view, the circumferentiallyopposite end sections 623 a of the increased width portion 623 arepositioned on the straight lines L1 interconnecting the center axis J1and the circumferentially opposite ends 622 a of the tip end portion622.

Since the stator core 221 a is provided with the slanted portion 624 asshown in FIG. 10, the tip end portion 622 is positioned higher than thecore-back 61. With this configuration, the axial existence range of thetip end portion 622 can radially overlap with the axial position of themagnetic center of the rotor magnet 32 indicated by a double-dot chainline.

As set forth above, the thickness of the slanted portion 624 in thedirection perpendicular or substantially perpendicular to the uppersurface 624 a is smaller than the axial thickness of the coil windingportion 621 and the core-back 61. Nevertheless, the magnetic path can besecured in the stator core 221 a by securing the circumferential widthof the slanted portion 624. It is also possible to secure the strengthof the teeth portions 62 and to reduce vibration of the stator 22. Inthe motor 12, the provision of the increased width portion 623 makes itpossible to prevent the winding of the coils 222 from collapsing.

Inasmuch as the inner edge section 624 b of the slanted portion 624 ispositioned radially outward of the inner edge section 623 b of theincreased width portion 623, it is possible to easily bend the statorcore 221 a as compared with a stator core having no slit.

FIG. 12 is an enlarged view showing a teeth portion 62 of a stator core221 b of a motor 12 according to a further related preferred embodimentof the present invention. When seen in a plan view, thecircumferentially opposite end sections 623 a of the increased widthportion 623 are parallel or substantially parallel to the straight lineL2 interconnecting the center axis J1 and the center of the tip endportion 622. The outer edge section 624 c of the slanted portion 624 andthe outer edge section 623 c of the increased width portion 623preferably have a linear shape perpendicular or substantiallyperpendicular to the straight line L2 when seen in a plan view.

FIG. 13 is a plan view showing the central portion 211 of the base plate21. In FIG. 13, the upper surface 215 of the base plate 21 is hatched byparallel slanted lines. This holds true in FIG. 14. The central portion211 preferably includes a plurality of protrusions 217 protruding upwardfrom the upper surface 215. The protrusions 217 are preferably formedby, for example, subjecting the base plate 21 to half blanking. Theangle between the two adjoining protrusions 217 about the center axis J1is preferably equal to or larger than about 90 degrees and smaller thanabout 180 degrees. Other structures of the motor 12 remain the same asthe structures of the motor 12 shown in FIG. 2.

FIG. 14 is a plan view showing the stator core 221 b attached to thebase plate 21. The protrusions 217 are inserted into the slits 625defined between the increased width portions 623 of the stator core 221b. The protrusions 217 are positioned radially inward of the inner edgesection 624 b of the slanted portion 624 to circumferentially engagewith the circumferentially opposite end sections 623 a of the increasedwidth portions 623. With this configuration, the position of the statorcore 221 b relative to the base plate 21 can be easily decided withinthe plane perpendicular or substantially perpendicular to the centeraxis J1.

In the motor 12, the magnetic path can be secured in the stator core 221b by securing the circumferential width of the slanted portion 624. Itis also possible to secure the strength of the teeth portions 62. Thisalso holds true in the preferred embodiments to be described later.

In the motor 12, even if a gap exists between the core-back 61 and thestator fixing portion 211 a, there is no need to perform positioning ofthe stator core 221 b relative to the base plate 21 through the use of ajig. With this configuration, it is possible to efficiently assemble themotor 12. In particular, if the base plate 21 including the statorfixing portion 211 a preferably is a single monolithic piece formed by,for example, a press work, the form error of the stator fixing portion211 a grows larger. This makes it necessary to leave a gap between thecore-back 61 and the stator fixing portion 211 a. Accordingly, it isadvisable to include the protrusions 217 in case where the base plate 21is formed by a press work.

FIG. 15 is a plan view showing another example of the stator core 221 cin accordance with a preferred embodiment of the present invention. Inthe stator core 221 c, there are preferably no increased width portionsprovided in any of the teeth portions 62. The stator core 221 cpreferably includes an annular core-back 61, a plurality of teethportions 62, and a plurality of lug portions 65. The lug portions 65extend radially inward from the core-back 61 within the planeperpendicular or substantially perpendicular to the center axis J1. Thelug portions 65 are preferably fixed by, for example, an adhesive agentto the outer circumferential surface of the stator fixing portion 211 ashown in FIG. 4. The lug portions 65 contact the upper surface 215 ofthe base plate 21 in the axial direction.

The core-back 61 is preferably a slanted portion 624 extending radiallyoutward and upward. Just like the slanted portion 624 shown in FIG. 10,the thickness of the core-back 61 in the direction perpendicular orsubstantially perpendicular to the upper surface of the core-back 61 issmaller than the axial thickness of the coil winding portion 621. Due tothe provision of the core-back 61 as the slanted portion 624, the axialexistence range of the tip end portion 622 can radially overlap with theaxial position of the magnetic center of the rotor magnet 32 as in thecase of FIG. 10.

FIG. 16 is a sectional view showing a motor 12 according to a firstpreferred embodiment of the present invention. In the motor 12, thenumber of core members 220 defining the core-back 61 of the stator core221 d and the section of the increased width portion 623 existingradially inward of the upper end of the slanted portion 624 ispreferably two, for example. The number of core members 220 defining thecoil winding portion 621, the tip end portion 622, and the section ofthe increased width portion 623 existing radially outward of the upperend of the slanted portion 624 is preferably five, for example. Otherstructures of the stator core 221 d preferably are the same as thestructures of the stator core 221 a shown in FIG. 10.

The portion 63 of the stator core 221 d provided radially inward of thelower end of the slanted portion 624, namely the section of theincreased width portion 623 and the core-back 61 provided radiallyinward of the slanted portion 624, is arranged below the hub portion 314of the rotor hub 31. In the following description, the portion 63 willbe referred to as “inner peripheral portion 63”. The core-back 61preferably axially contacts a projection 218 defined on the uppersurface 215 of the central portion 211 of the base plate 21. The upperend of the stator fixing portion 211 a is preferably positioned inwardof the hub portion 314 and upward of the lower end of the hub portion314. The lower section of the inner circumferential surface of the hubportion 314 preferably includes a slanted surface 314 a inclinedradially outward and downward. The upper section of the outercircumferential surface of the stator fixing portion 211 a preferablyincludes a slanted surface 211 b inclined radially outward and downward.

A slanted gap 71 inclined radially outward and downward is preferablydefined between the slanted surface 314 a of the hub portion 314 and theslanted surface 211 b of the stator fixing portion 211 a. In thefollowing description, the slanted gap 71 will be referred to as “firstcommunication gap 71”. A second communication gap 72 radially widenedfrom the first communication gap 71 is defined between the lower end ofthe hub portion 314 and the inner peripheral portion 63 of the statorcore 221 d axially opposed to the hub portion 314. Preferably, theradial width of the second communication gap 72 is a little larger thanthe radial width of the core-back 61 shown in FIG. 9, namely the radialwidth between the inner edge section of the core-back 61 and the innerend of the slit 625.

The sleeve housing 43 preferably includes a slanted surface 431 aprovided in the upper section of the outer circumferential surface ofthe cylinder portion 431 and inclined radially inward and downward. Asubstantially cylindrical cylinder gap 474 is defined between theslanted surface 431 a and the inner circumferential surface of the hubportion 314. A seal region 474 a in which the boundary surface of alubricant 46 is preferably provided is defined in the cylinder gap 474.The cylinder gap 474 is connected to a space around the stator 22 viathe first communication gap 71 and the second communication gap 72. Thewidth of the first communication gap 71 is preferably smaller than theradial maximum width of the cylinder gap 474 at the lower end 431 b ofthe slanted surface 431 a.

In the motor 12, the provision of the first communication gap 71 andsecond communication gap 72 makes it possible to prevent orsubstantially prevent the lubricant 46 from being vaporized from theseal region 474 a. Since the width of the first communication gap 71 issmaller than the radial maximum width of the cylinder gap 474, it ispossible to further prevent vaporization of the lubricant 46.

By reducing the axial thickness of the core-back 61, it becomes possibleto arrange the core-back 61 in a narrow space between the hub portion314 and the base plate 21, thereby reducing the size of the motor 12. Bymaking the axial thickness of the coil winding portion 621 larger thanthe axial thickness of the core-back 61, it is possible to improve theelectromagnetic characteristics.

FIG. 17 is a view showing a motor according to one modified example of apreferred embodiment of the present invention. In the motor 12, a firstcommunication gap 73, i.e., an axially-extending vertical gap, isdefined between the lower section of the inner circumferential surfaceof the hub portion 314 and the upper section of the outercircumferential surface of the stator fixing portion 211 a. The radialwidth of the first communication gap 73 and the axial width of thesecond communication gap 72 are preferably smaller than the radialmaximum width of the cylinder gap 474. With this configuration, it ispossible to further prevent the lubricant 46 from being vaporized fromthe cylinder gap 474.

FIG. 18 is a view showing a motor 12 according to a second preferredembodiment of the present invention. A bearing mechanism 4 a of themotor 12 preferably includes a single sleeve bearing portion 49 made of,for example, a metal material. A radial gap 471 is defined between theinner circumferential surface of the bearing portion 49 and the outercircumferential surface of the shaft portion 41. At the upper side ofthe radial gap 471, a seal region 475 is preferably defined between theupper section of the inner circumferential surface of the bearingportion 49 and the upper section of the outer circumferential surface ofthe shaft portion 41. The lower section of the outer circumferentialsurface of the bearing portion 49 is inserted into the stator fixingportion 211 a of the base plate 21. A substantially cylindrical cylindergap 641 is defined between the upper section of the outercircumferential surface of the bearing portion 49 and the hub portion314 of the rotor hub 31. The cylinder gap 641 is connected to the sealregion 475 through a gap 642 radially extending between the uppersurface of the bearing portion 49 and the lower surface of the coverportion 311 of the rotor hub 31 positioned radially inward of the hubportion 314. Other structures of the motor 12 preferably remain the sameas the structures of the motor 12 shown in FIG. 16.

In the motor 12, the gap 642, the cylinder gap 641, the firstcommunication gap 71, and the second communication gap 72 are definedbetween the seal region 475 and the space around the stator 22. It istherefore possible to further prevent the lubricant 46 from beingvaporized from the seal region 475. In the motor 12, a firstcommunication gap 73 which is a vertical gap may also be provided as isthe case in FIG. 17.

While certain preferred embodiments of the present invention have beendescribed above, the present invention is not limited to the foregoingpreferred embodiments but may be modified in many different forms. Forexample, in the foregoing preferred embodiments, it is only necessarythat the slanted surface 511 a be provided in at least the portion ofthe upper edge 511 of the substrate insertion hole 51 making contactwith the connection portion 231 and further that the slanted surface 512a be provided in at least the portion of the lower edge 512 makingcontact with the lead portion 232. With this configuration, it ispossible to easily insert the lead portion 232 into the substrateinsertion hole 51. Instead of the slanted surfaces 511 a and 512 a,curved bulging surfaces may alternatively be provided in the upper edge511 and the lower edge 512, respectively.

The substrate insertion hole 51 may be arranged so that the loweropening thereof can be included in the peripheral portion 212 positionedlower than the step portion 213. As long as the lead portion 232 isarranged below the peripheral portion 212 through the substrateinsertion hole 51, at least a portion of the lower opening of thesubstrate insertion hole 51 may be included in the step portion 213 orthe peripheral portion 212. In the motor 12, at least some portions ofthe solder portions 233 are positioned within the solder reception holes52. This makes it possible reduce the height of the motor 12.

In the motor 12 shown in FIG. 4, the connection portion 231 of thesubstrate 23 may be adhesively bonded to the lower sections of the coils222. In this case, prior to attaching the stator 22 and the substrate 23to the base plate 21, the upper surface of the connection portion 231 isadhesively bonded to the coils 222 and the lead wires 223 are solderedto the lower surface of the connection portion 231. The outlet holes 231b and the solder portions 233 need not necessarily overlap with eachother in the axial direction. In that case, the outlet holes 231 b maypreferably be closed by an adhesive agent or the like, for example. Thelower surface of the connection portion 231 may be adhesively bonded tothe upper surface 215 of the central portion 211. In that case, it ispreferred that the stator 22 be attached to the base plate 21 after thelower surface of the connection portion 231 is adhesively bonded to theupper surface of the central portion 211.

In the preferred embodiments described above, a cutout portion may beprovided in the connection portion 231. The lead wires 223 may be led tothe lower surface of the connection portion 231 through the cutoutportion. In the motor 12, the adhesive agent 24 need not be necessarilyfilled into the solder reception holes 52. The solder reception holes 52may be closed by the seal member 45 to prevent leakage of a gas. Theseal member 45 may be brought into contact with the solder portions 233to press the solder portions 233 upward. With this configuration, it ispossible to prevent the solder portions 233 from being extruded out ofthe solder reception holes 52.

The base plate 21 may be formed by, for example, a cutting work ratherthan a press work. Since the upper section of the step portion 213exists at least in the section of the lower surface of the base plate 21where the lead portion 232 exists, the lead portion 232 is preventedfrom protruding downward from the base plate 21. The stator fixingportion 211 a may be provided independently of the base plate 21.

In the motor 12 shown in FIG. 2, the shaft portion 41 may be providedindependently of the rotor hub 31. In that case, the shaft portion 41 ispreferably fixed to the rotor hub 31 by, for example, press-fitting orother desirable methods. In the motors 12 shown in FIGS. 2 and 16, thethrust dynamic pressure groove array may be provided on the uppersurface of the cylinder portion 431 of the sleeve housing 43. In therelated preferred embodiments described above, the stator core may beindirectly fixed to the stator fixing portion 211 a through an annularmember.

The technique of providing the solder reception holes in the base platemay be applied to a motor of a large-size disk drive apparatus holding aplurality of disks.

In the stator core 221 a shown in FIG. 9, as can be noted from a planview shown in FIG. 19, the circumferential opposite end sections 621 bof the coil winding portion 621 of each of the teeth portions 62 may becurved to extend radially outward from the center of the coil windingportion 621 toward the circumferential opposite sides. Thecircumferential opposite end sections 621 b of the coil winding portion621 are connected to the circumferentially opposite ends 622 a of thetip end portion 622. The circumferential width of the increased widthportion 623 and the tip end portion 622 is larger than the width of thenarrowest section, i.e., the radial inner section, of the coil windingportion 621. In the stator core 221 a including the teeth portions 62shown in FIG. 19, the provision of the increased width portion 623 makesit possible to secure a magnetic path within the stator core 221 a.Since the circumferential width of the tip end portion 622 and thecircumferential minimum width of the increased width portion 623 arelarger than the minimum width of the coil winding portion 621, it ispossible to efficiently prevent the magnetic flux from gettingsaturated. It is however more desirable that the circumferential widthof the tip end portion 622 and the circumferential minimum width of theincreased width portion 623 be larger than the maximum width of the coilwinding portion 621. This holds true in other preferred embodimentsdescribed above.

In the stator core 221 a, when seen in a plan view, thecircumferentially opposite end sections 623 a of the increased widthportion 623 are positioned on the straight lines L1 interconnecting thecenter axis J1 and the circumferentially opposite ends 622 a of the tipend portion 622. Alternatively, the circumferentially opposite endsections 623 a of the increased width portion 623 may be positionedcircumferentially outward of the straight lines L1, namely at theopposite sides of the straight lines L1 from the center of the tip endportion 622. The radial inner end of the slit 625 may be positioned alittle radially outward of the inner edge section 424 b of the slantedportion 424. In the stator core 221 a, the increased width portion 623as a whole may be a slanted portion. As shown in FIG. 14, theprotrusions 217 provided on the base plate 21 may be inserted into theslits 625 to fix the position of the stator core 221 a relative to thebase plate 21 in the plane substantially perpendicular to the centeraxis J1.

The number of the projections 217 of the base plate 21 is not limited tothree but may alternatively be two or other numbers greater than three.The angle between at least one set of adjoining projections 217 amongthe plurality of projections 217 is preferably equal to or larger thanabout 90 degrees and smaller than about 180 degrees. If the number ofthe protrusions 217 is two, it is preferred that the angle between thetwo projections 217 about the center axis J1 be equal to about 180degrees. Pins inserted into through-holes defined in the base plate 21may be used as the protrusions. Two or more cutout portions 612 may beprovided in the core-back 61. In that case, the protrusions of the baseplate 21 may be inserted into the cutout portions 612, thereby fixingthe position of the stator core 221 a relative to the base plate 21 inthe plane perpendicular to the center axis J1.

In the stator core 221 c shown in FIG. 15, only a portion of thecore-back 61 may be an annular slanted portion. In the first and secondpreferred embodiments, the number of the core members 220 defining thecore-back 61 of the stator core 221 d and the section of the increasedwidth portion 623 existing radially inward of the upper end of theslanted portion 624 may be three or four rather than two. The axialthickness of the teeth portions 62 and the axial thickness of thecore-back 61 may be equal to each other, as long as the firstcommunication gaps 71 and 73 and the second communication gap 72 can beprovided.

The configurations of the above-described preferred embodiments andmodifications thereof may be appropriately combined unless contradictoryto one another.

The preferred embodiments of the present invention can be used as amotor for a disk drive apparatus and as a motor for an apparatus otherthan the disk drive apparatus.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A motor, comprising: a stationary unit; a rotary unit; and a bearing mechanism arranged to support the rotary unit so as to rotate with respect to the stationary unit about a center axis extending in an up-down direction; wherein the rotary unit includes a cover portion extending around the center axis, a cylindrical sidewall portion extending downward from an outer edge of the cover portion, a tubular hub portion protruding downward from the cover portion at a radial inner side of the sidewall portion and a rotor magnet fixed to an inner circumferential surface of the sidewall portion; the bearing mechanism includes a shaft portion extending downward from the cover portion along the center axis and a bearing portion to which the shaft portion is inserted, the bearing portion being arranged to support the shaft portion through a lubricant, the bearing portion including an upper section positioned radially inward of the hub portion; the stationary unit includes a stator positioned radially inward of the rotor magnet, a base portion positioned below the stator and a stator fixing portion having a substantially cylindrical shape to extend upward from a central portion of the base portion, the stator fixing portion including an upper end positioned inward of the hub portion and higher than a lower end of the hub portion; the stator includes a stator core and a plurality of coils; the stator core includes an annular core-back arranged below the hub portion and a plurality of teeth portions extending radially outward from the core-back; each of the teeth portions includes a coil winding portion wound with each of the coils and a slanted portion positioned between the core-back and the coil winding portion to extend radially outward and upward; a seal region in which a boundary surface of the lubricant is provided is defined between the upper section of the bearing portion and the rotary unit; a substantially cylindrical cylinder gap is defined between an inner circumferential surface of the hub portion and an outer circumferential surface of the upper section of the bearing portion; a first communication gap is defined between a lower section of the hub portion and an upper section of the stator fixing portion, the first communication gap including a section extending in an axial direction or inclined radially outward and downward; and a second communication gap is defined between the lower end of the hub portion and a radial inner section of the stator core, the second communication gap extending radially outward from the first communication gap.
 2. The motor of claim 1, wherein the seal region is defined in the cylinder gap.
 3. The motor of claim 2, wherein the seal region is defined between an inner circumferential surface of the upper section of the bearing portion and an outer circumferential surface of the upper section of the shaft portion, the seal region being radially connected to the cylinder gap at an upper side of the bearing portion.
 4. The motor of claim 3, wherein the core-back has an axial thickness smaller than an axial thickness of the coil winding portion of each of the teeth portions.
 5. The motor of claim 1, wherein the seal region is defined between an inner circumferential surface of the upper section of the bearing portion and an outer circumferential surface of the upper section of the shaft portion, the seal region being radially connected to the cylinder gap at an upper side of the bearing portion.
 6. The motor of claim 5, wherein the core-back has an axial thickness smaller than an axial thickness of the coil winding portion of each of the teeth portions.
 7. The motor of claim 1, wherein the core-back has an axial thickness smaller than an axial thickness of the coil winding portion of each of the teeth portions.
 8. The motor of claim 7, wherein the coil winding portion includes five steel plates stacked one above another, and the core-back includes two, three or four steel plates stacked one above another.
 9. The motor of claim 1, wherein the first communication gap has a width smaller than a radial maximum width of the cylinder gap.
 10. The motor of claim 1, wherein the second communication gap has a radial width larger than a radial width of the core-back.
 11. The motor of claim 1, wherein the base portion and the stator fixing portion are defined a single monolithic member.
 12. A disk drive apparatus, comprising: the motor of claim 1 arranged to rotate a disk; an access unit arranged to perform at least one of an information reading task and an information recording task with respect to the disk; and a housing arranged to accommodate the disk, the motor and the access unit. 